The present invention relates to a method for injection of waste materials in subsurface formations via drilled holes in the ground, where the materials are mixed with water before injection.
This invention more specifically relates to such a method where the waste materials at least comprise relatively large solid particles, for instance represented by drill cuttings.
It is earlier known using a similar method to dispose of harmful materials in excisting oil wells below water. Such solutions are for instance mentioned in the newspaper article "Toxic waste could be hurried in old oil wells" by Jane Bird in Sunday Times, Aug. 19, 1990.
The earlier known method has only been used in connection with liquid waste materials. When such liquids has been diluted with water, this has primarily been done to disolve the liquids to reduce risks during handling. However the known method has not been used for waste materials comprising large amounts of solid materials.
The subsurface formation in which the waste materials earlier have been injected, are substantially porous structures where solid matters which possibly are introduced shortly will clog the pores in said structure and thus prevent or impede further intrusion. As far as we know attempts of such injection of materials comprising solid particles in subsurface formations have not been undertaken. If such attempts should be made it should probably give the result that only small amounts of any waste material could be forced into the structure because the pores would be clogged by solid particles when such are present, and this clogging should prevent further filling of the structure. It should also be mentioned that such experiments including injection are very expensive and cannot be undertaken if real and good expectations do not exist.
The object of the present invention is to obtain a method according to which injection of waste materials including relatively large amounts of coarse solid particles into subsurface formations, in such a manner that the waste into subsurface formations, in such a manner that the waste materials can be rendered harmless for all future. This is obtained as the waste materials are transformed in such a manner that they after the transformation may be injected in large amounts in existing subsurface formations and structures without the above disadvantages. By using the method according to the present invention it would be possible to obtain an injection of waste materials of the type mentioned above into subsurface formations and structures so that these formations substantially or completely will be filled by the injected waste materials without any considerable space left empty. Large amounts of waste material comprising considerable amounts of solid matters therefore may be injected into porous formations and structures as layers of sand, clay, or stone, and in existing pockets. The method according to this invention may also be used to squeeze remaining fragments of oil and gas out from a production well, for instance by injecting the waste materials in an adjacent well on the same oil field.
This invention in particular relates to a method treating drill cuttings during oil- and gas-drilling, also in connection with oil- and gas-wells below water, as the method results in a safe and permanent deposition of drill cuttings without giving detrimental effects on the environment.
The problem related to disposal of bore cuttings which are surfacing during drill operation has been aproached in many different manners. According to many of the previous methods large efforts have been made to clean the drill cuttings to regain valuable consistuents therefrom. Among earlier suggested solutions the following may be mentioned: cleaning by washing with sea water, pelleting, storing in a wide, vertical tube arranged on the sea bottom to be filled with drill cuttings from above and possibly with removal of oil components released in the tube. Attempts have also been made in which the drill cuttings are grinded in a mill. This is done in hope that frictional heat developed during the grinding process will evaporate the oil components and removed therefrom the drill cuttings.
The present invention aims at a complete and final treatment of drill cuttings surfacing during a drilling process. The treatment of the drill cuttings are not cleaned previous to the deposition process, but are disintegrated by crushing while all its ingredients remains intact. The crushing process is repeated until particles above a certain predetermined size no longer exist. From these particles a dispersion and/or an emulsion in water is produced. This dispersion may be disposed of in existing, subsea structures at a pressure required for the structure of the formations at the site and the depth at which the depositing is undertaken.
Earlier known methods for depositing drill cuttings have first of all led to great contamination problems. These problems are increasing and have recently overruled the cost and time aspects of these proceedings. The object of the present invention is to obtain a method for treating and depositing drill cuttings, that over comes to which the earlier known problems, where the costs and the required treatment time are to lower than previously obtained.
When the expression injection is used this also assumes that the waste materials advantageously can be led back to the site in which they initially were found. However the method may also be used to deposit the waste material in places from which other materials are removed, or possibly in special wells produced in stable and suitable formations or in weak and crumbeling zones.
In using a method according to the present invention waste materials are injected in subsurface formations as the waste materials first mixed with liquids and then are injected into subsurface formations, via drilled holes or wells in the ground.
The features for the present invention include
the waste materials, including relatively large solid particles, are crushed and then washed out in a liquid to form a dispersion, PA1 the larger particles in the dispersion enter a feedback loop to be chrushed again, PA1 at least one portion of the finished dispersion is brought to circulate in the process at the same time as more solid matter is added so that a thickening of the dispersion is obtained, and PA1 that the dispersion, when stabilized and when it no longer comprises redundant amounts of liquids, is injected at a suitable pressure into the subsurface formations.